In the framework of the coding of multi-channel audio signals, two approaches are particularly well known and used.
The first and oldest consists in matrixing the channels of the original multi-channel signal in such a manner as to reduce the number of signals to be transmitted. By way of example, the Dolby® Pro Logic® II multi-channel audio coding method carries out the matrixing of the six channels of a 5.1 signal into two signals to be transmitted. Several types of decoding can be applied in order to reconstruct as faithfully as possible the six original channels.
The second approach, called parametric audio coding, is based on the extraction of spatialization parameters in order to reconstruct the spatial perception of the listener. This approach is mainly based on a method called “Binaural Cue Coding” (BCC) which aims, on the one hand, to extract then to code the indices of the hearing localization and, on the other hand, to code a monophonic or stereophonic signal coming from the matrixing of the original multi-channel signal.
In addition, there is one approach, hybrid of the two above approaches, based on a method called “Principal Component Analysis” (PCA). Indeed, PCA can be seen as a dynamic matrixing of the channels of the multi-channel signal to be coded. More precisely, the PCA is obtained by rotation of the data whose angle corresponds to the spatial position of the dominant sound sources, at least for the stereophonic case. This transformation is furthermore considered as the optimal decorrelation method that allows the energy of the components of a multi-component signal to be compacted. One example of stereophonic audio coding using PCA is disclosed in the documents WO 03/085643 and WO 03/085645.
However, the PCA carried out according to the prior art does not allow a precise characterization of the signals to be coded and, consequently, the energy of the signals coming from this analysis is not compacted enough in the principal component.